A separation device is necessary to obtain hydrogen from hydrogen mixed gas, and purification of hydrogen is possible by using a variety of separation processes using pressure swing adsorption (PSA), subzero cooling, a separation membrane, or a getter. Since there is an advantage of high energy efficiency by configuring a process using a palladium-based separation membrane in the hydrogen purification technology, a lot of research is under way in this field.
For the performance of a hydrogen separation membrane, hydrogen flux and selectivity are the most important indicators, so a lot of research and effort are being made in domestic and foreign countries for the improvement of such performance. In particular, because the hydrogen penetration rate is determined by the thickness of a hydrogen separation membrane layer, research for coating the ultra-thin membrane of dense material without fine pores is under way.
When a palladium-based alloy is made into an ultra-thin membrane, the effects of the loss and the composition change of the hydrogen separation membrane are increased all the more due to the thermal safety and the attachment of fine dust that can be introduced during the process. That is, whereas a composition change of a maximum of 10% can be expected when pollutants of 1 μm diameter are attached on the surface of a coated separation membrane of 10 μm thickness, a composition change of a maximum of 50% can be expected when particulate pollutants of 1 μm diameter are attached on the surface of a coated membrane of 1 μm thickness. Therefore, it is an obvious phenomenon that the extent of effect by pollutants is further increased as the hydrogen separation membrane becomes thinner.
Recently, there are many attempts to configure a reaction-separation concurrent process by providing a hydrogen separation membrane inside the reactor. In particular, by removing hydrogen, which is a product, for the main purpose of developing the hydrogen manufacturing process using coal or naphtha, the equilibrium conversion rate is facilitated in the normal direction (Reaction Formula 1). Such a reactor uses hydrocarbon as fluidized gas and a micro-catalyst as an in-layer substance, so that, research on a fluidized-bed reactor that maximises contact between the hydrocarbon and the catalyst and also maximizes the heat transfer efficiency is under way (MRT Company of Canada). For the reactor having this configuring, “suppressing the contact between the separation membrane and the particulates is an absolutely necessary condition.CH4H2OCO3H2, Heat of reaction=206 kJ/mol  [Reaction Formula 1]
From examining the papers and precedent patents in the prior art related to the research and development of the separation membrane protective layer by coating porous ceramic materials, metals and ceramic materials on the surface of the hydrogen separation membrane, a technique of composing an ultrathin membrane layer is still at an incomplete stage, and there are no research results from the attempt to place a protective layer on the surface thereof. The only patent (Japanese Patent Laid-Open 2004-176128) that was disclosed is about the concept that resistance to oxygen can be increased and brittleness to hydrogen can be improved by binding a dense foil sheath of palladium-silver composite material on an outside of a foil-type separation membrane.
Therefore, the technological development of these fields is indispensable since it is possible to maintain for a long time a high selectivity and permeability for hydrogen when the development of an ultrathin coating technique, for manufacturing hydrogen separation membranes, and the development of a protective layer, for protecting the ultrathin separation membrane without a decrease of hydrogen penetration performance, are made simultaneously.